U.S. Pat. No. 4,823,113 discloses a ferromagnetic marker capable of generating both even and odd higher harmonics of the frequency of the exciting field, which is made from a glassy metal with Perminvar properties. Glassy alloys which can exhibit Perminvar characteristics have the composition Co.sub.a Fe.sub.b Ni.sub.c M.sub.d B.sub.e Si.sub.f, where M is at least one element selected from the group consisting of Cr, Mo, Mn and Nb, where "a" ranges from about 66 to 71 atomic %, "b" ranges from about 2.5 to 4.5 atomic %, "c" ranges from about 0 to 3 atomic %, "d" ranges from about 0 to 2 atomic % except when M=Mn in which case "d" ranges from about 0 to 4 atomic %, "e" ranges from about 6 to 24 atomic %, and "f" ranges from about 0 to 19 atomic %. The Perminvar characteristics are imparted by heat treating the alloy at a temperature between about 50.degree. and 110.degree. C. below the first crystallization temperature of the alloy for a time period between about 15 and 180 minutes and then cooling to room temperature at a rate slower than about -60.degree. C./min. The '113 patent discloses that these alloys are particularly useful in the manufacture of harmonic tags.
Near-zero magnetostriction alloys having the composition Co.sub.70.3 Fe.sub.4.7 Si.sub.15 B.sub.10 and annealed in the presence of an external field applied perpendicular to the ribbon plane to impart a hysteresis loop having a pinched, discontinuous change about the origin have been reported in Domain Patterns and High-Frequency Magnetic Properties of Amorphous Metal Ribbons, H. J. de Wit and M. Brouha, J.Appl.Phys., 57, 3560-63 (1985).
Introduction to Magnetic Materials, Addison-Wesley Publishing Co., B. D. Cullity, 1972, pg 340 discloses theoretically generated hysteresis loops having a pinched shape with an abrupt discontinuous change about the origin. B-H loops are proposed for each of the possible directions the magnetization could have in relation to the plane of the ribbon, but no process is disclosed for imparting a desired loop shape.
M. Imamura and T. Sasaki, Perpendicular Anisotropy Induced in Fe-Ni Amorphous Ribbons Containing Phosphorus, IEEE Transactions of Magnetics, MAG-20, 3185-87 (1985) discusses the origin of anisotropy perpendicular to the ribbon surface in Fe-Ni amorphous ribbons containing phosphorus. The anisotropy is induced via annealing in an H.sub.2 or N.sub.2 atmosphere, and was not observed in ribbons having Fe-Ni-B, Fe-B, Fe-Si-B or Co-Ni-Si-B compositions. The perpendicular anisotropy was attributed to a chemical change at the surface.
H. C. Fiedler, J. D. Livingston and S. C. Huang, The Deleterious Effect of Aluminum in Fe-B-Si-C Amorohous Ribbon, J. Mag. & Mag. Mat. 26, 157 (1982) attributed the degradation of the magnetic properties of the Fe-B-Si-C based alloys upon the presence a thin layer of crystalline material on the top surface of the as-cast ribbon which is believed to cause an out-of-plane anisotropy in the alloys.
J. D. Livingston, Magnetic Domains, Anisotropies and Properties of Amorphous Metals. GE Technical Information Series, Report No. 85CRD146, pg. 5 (August 1985) discloses introducing a magnetic easy axis normal to the ribbon plane by annealing the alloy strip in a large perpendicular field. The permeability of the annealed alloys is high at high frequencies. Upon annealing coercivity and hysteresis losses increase but eddy-current losses are reduced.
A number of patents disclose annealing metallic alloys which are at least about 90% amorphous and have compositions which are generally represented by Fe.sub.a Co.sub.b B.sub.c Si.sub.d C.sub.e. The alloys of U.S. Pat. No. 4,834,815 have about 75 to about 85 atomic % iron ("a"), about 0.1 to about 0.8 atomic % Co ("b"), about 12 to about 15 atomic % B ("c"), about 2 to about 5 atomic % Si ("d"), and about 1 to about 3 atomic % C ("e"). The alloys may be annealed at a temperature between about 300.degree. C. and 400.degree. C. The cooling rate is between about 0.5.degree. C./min. and about 75.degree. C./min, with about 10.degree. C. to about 15.degree. C./min. being most preferred. U.S. Pat. Nos. 4,219,335, 4,249,969 and 4,298,409 disclose alloys with compositions ranging from 80.0 to 82.0 atomic % iron ("a"), 12.5 to 14.5 atomic % boron ("c"), 2.5 to 5.0 atomic % silicon ("d") and 1.5 to 2.5 atomic % carbon. Each patent discloses an annealing step at temperatures between about 340.degree. C. and 385.degree. C., followed by a cooldown at a rate of about 0.5.degree. C./min. to about 75.degree. C./min., with a rate of about 1.degree. C./min. to about 16.degree. C./min. being preferred. The annealing step further reduces core loss and volt-ampere demand, making the alloys particularly suitable for use in transformer cores.
U.S. Pat. No. 4,268,325 discloses double annealing a magnetic glassy metal alloy sheet having a composition which is between 70 to 90 atomic % of at least one metal selected form the group consisting of iron and cobalt, up to about three-fourths of which may be replaced by nickel and up to about one quarter of which may be replaced by one or more metal selected from the group consisting of vanadium, chromium, manganese, copper, molybdenum, niobium, tantalum, and tungsten, and the balance at least one metalloid selected from the group consisting of boron, carbon and phosphorus, up to about three-fifths of which may be replaced by aluminum, plus incidental impurities. The first anneal is conducted between about 225.degree. C. and the glass transition temperature, which is the temperature below which the viscosity of the glass exceeds 10.sup.14 poise. The second anneal is conducted at a temperature which is between about 25.degree. C. and 100.degree. C. lower than the first annealing temperature. The cooldown rate following the annealing step is between about 0.1.degree. C./min and 100.degree. C./min., and preferably between 0.5.degree. C./min. and 5.degree. C./min. The annealed magnetic glassy metal alloy sheets exhibit low magnetization losses making them particularly suitable for transformer cores.
U.S. Pat. No. 4,881,989 discloses near zero magnetostrictive alloys having the composition (Fe.sub.1-.alpha. M.sub..alpha.).sub.100-x-y-z-a Cu.sub.x Si.sub.y,B.sub.z M'.sub.a and containing nanocrystalline structure and a process for making nanocrystalline alloys having low magnetostriction. The alloys are cast to form a substantially amorphous alloy, annealed at a temperature of about 550.degree. C. for 1 hour, with or without an applied field and cooled. Cooling rates up to 600.degree. C. per minute are disclosed. Low core losses were reported for wound cores annealed at 550.degree. C. for 1 hour and cooled in air. Other cores annealed under same conditions gave a rounded dc loop.